US10687742B2ActiveUtilityA1
Using invariant factors for pulse oximetry
Est. expiryJun 12, 2035(~8.9 yrs left)· nominal 20-yr term from priority
A61B 5/7214A61B 5/14552A61B 5/6826
87
PatentIndex Score
15
Cited by
148
References
18
Claims
Abstract
An example method for performing pulse oximetry can commence with receiving at least three light signals of three different wavelengths reflected from a human tissue. The human tissue includes a pulsatile tissue and a non-pulsatile tissue. Based on the three light signals, values of at least three functions are determined. The three functions are invariant to an oxygen saturation in the pulsatile tissue and depend on location of a sensor operable to detect the three light signals and pressure of the sensor on the human tissue. Based on the values of the three functions, non-pulsatile components are analyzed for intensities of a red light signal and infrared light signal reflected from the human tissue. The non-pulsated components are removed from the intensities to allow correct estimates of a ratio of the absorption coefficients, with the ratio being used to determine the oxygen saturation in the pulsatile tissue.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1. A method for performing a pulse oximetry, the method comprising:
receiving, by an optical sensor of a wearable device configured to be worn by a patient:
a red light signal reflected from a human tissue of the patient, the human tissue including a pulsatile tissue and a non-pulsatile tissue, the red light signal being associated with a red wavelength;
an infrared light signal reflected from the human tissue, the infrared light signal being associated with an infrared wavelength; and
a third light signal reflected from the human tissue, the third light signal being associated with a third wavelength, the third wavelength being different from the red wavelength and the infrared wavelength;
determining, by a processor communicatively coupled with the sensor and based on the red light signal, a first value of a first function invariant to an oxygen saturation in the pulsatile tissue;
determining, by the processor and based on the infrared light signal, a second value of a second function invariant to the oxygen saturation in the pulsatile tissue;
determining, by the processor and based on the third light signal, a third value of a third function invariant to the oxygen saturation in the pulsatile tissue;
determining, by the processor, a first additive component in the red light signal and a second additive component in the infrared light signal, wherein the determining is based on the first value, the second value, and the third value, and wherein the first additive component and the second additive component are due to a reflection from the non-pulsatile tissue;
removing, by the processor, the first additive component from an intensity of the red light signal to estimate a first corrected intensity;
removing, by the processor, the second additive component from an intensity of the infrared light signal to estimate a second corrected intensity;
calculating, by the processor and based on the first corrected intensity and the second corrected intensity, a ratio of a red light absorption coefficient and an infrared light absorption coefficient;
determining, by the processor and based at least partially on the ratio, at least the oxygen saturation in the pulsatile tissue;
acquiring, by the processor, a reference photoplethysmogram (PPG) waveform;
determining, by the processor, first similarity measures between a pre-determined number of waveforms of the red light signal and the reference PPG waveform;
determining, by the processor, second similarity measures between a pre-determined number of waveforms of the infrared light signal and the reference PPG waveform, the waveforms of the infrared light signal being detected concurrently with the waveforms of the red light signal;
calculating, by the processor, an average of products Ai×Bi to estimate an adequacy of the red light signal and the infrared light signal, wherein Ai are the first similarity measures, Bi are the second similarity measures, and i=1, . . . , N, wherein N is the pre-determined number of waveforms of the red light signal;
estimating, by the processor, an estimate of the adequacy of the red light signal and the infrared light signal, based on the average of products;
collecting, by the processor and for a period of time, data concerning the red light signal, the infrared light signal, the third light signal, the adequacy, and the oxygen saturation;
analyzing, by the processor, the data to detect trends in the oxygen saturation; and
providing, by the processor and based on the trends in the oxygen saturation, reports regarding a health status of the patient.
2. The method of claim 1 , wherein the pulsatile tissue includes an artery and the non-pulsatile tissue includes skin.
3. The method of claim 1 , wherein the human tissue includes one of the following: a fingertip, a wrist, an ankle, a neck, a chest, and an earlobe.
4. The method of claim 1 , wherein the third light signal includes an isosbestic light signal, the isosbestic light signal including one of a near infrared light signal and a green light signal.
5. The method of claim 1 , wherein the first value is a maximum of the intensity of the red light signal, the second value is a maximum of the intensity of the infrared light signal, and the third value is a maximum of an intensity of the third light signal.
6. The method of claim 1 , wherein the first additive component and the second additive component are determined based on an empirically-derived lookup table.
7. The method of claim 1 , further comprising mapping physical conditions, the physical conditions including a location of the optical sensor relative to the human tissue and a pressure of the optical sensor on the human tissue, to values of the first function, values of the second function, and values of the third function by repeatedly performing the following operations:
receiving, by the processor, an indication that the physical conditions are changed due to displacing the optical sensor relative to the human tissue;
detecting, by the optical sensor, the red light signal, the infrared light signal, and the third light signal for a predetermined period of time;
determining, by the processor and based on the red light signal, a value of the first function;
determining, by the processor and based on the infrared light signal, a value of the second function; and
determining, by the processor and based on the third light signal, a value of the third function.
8. The method of claim 1 , wherein the reference PPG waveform is obtained based on a PPG measured from a fingertip.
9. The method of claim 1 , wherein at least one of the first similarity measures is determined using
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wherein {right arrow over (w)} is data representing the waveform of the red light signal, and {right arrow over (ƒ)} is data representing the reference PPG waveform.
10. A system for performing a pulse oximetry, the system comprising:
at least one optical sensor of a wearable device, the wearable device being configured to be worn by a patient; and
at least one processor communicatively coupled to the at least one optical sensor; and wherein:
the at least one optical sensor is configured to detect:
a red light signal reflected from a human tissue of the patient, the human tissue including a pulsatile tissue and a non-pulsatile tissue, the red light signal being associated with a red wavelength;
an infrared light signal reflected from the human tissue, the infrared light signal being associated with an infrared wavelength; and
a third light signal reflected from the human tissue, the third light signal being associated with a third wavelength, the third wavelength being different from the red wavelength and the infrared wavelength; and
the at least one processor is configured to:
determine, based on the red light signal, a first value of a first function invariant to an oxygen saturation in the pulsatile tissue;
determine, based on the infrared light signal, a second value of a second function invariant to the oxygen saturation in the pulsatile tissue;
determine, based on the third light signal, a third value of a third function invariant to the oxygen saturation in the pulsatile tissue;
determine a first additive component in the red light signal and a second additive component in the infrared light signal, wherein the determination is based on the first value, the second value, and the third value, and wherein the first additive component and the second additive component are due to reflection from the non-pulsatile tissue;
remove the first additive component from an intensity of the red light signal to estimate a first corrected intensity;
remove the second additive component from an intensity of the infrared light signal to estimate a second corrected intensity;
calculate, based on the first corrected intensity and the second corrected intensity, a ratio of a red light absorption coefficient and an infrared light absorption coefficient;
determine, based at least partially on the ratio, at least the oxygen saturation in the pulsatile tissue;
acquire a reference photoplethysmogram (PPG) waveform;
determine first similarity measures between a pre-determined number of waveforms of the red light signal and the reference PPG waveform;
determine second similarity measures between a pre-determined number of waveforms of the infrared light signal and the reference PPG waveform, the waveforms of the infrared light signal being detected concurrently with the waveforms of the red light signal;
calculate an average of products Ai×Bi to estimate an adequacy of the red light signal and the infrared light signal, wherein Ai are the first similarity measures, Bi are the second similarity measures, and i=1, . . . , N, wherein N is a pre-determined number of waveforms of the red light signal;
estimate, by the processor, an estimate of the adequacy of the red light signal and the infrared light signal, based on the average of products;
collect, for a period of time, data concerning the red light signal, the infrared light signal, the third light signal, the adequacy, and the oxygen saturation;
analyze the data to detect trends in the oxygen saturation; and
provide, based on the trends in the oxygen saturation, reports regarding a health status of the patient.
11. The system of claim 10 , wherein the at least one optical sensor is configured to be placed on one of the following: a fingertip, a wrist, an ankle, a neck, a chest, and an earlobe.
12. The system of claim 10 , wherein the third light signal includes an isosbestic light signal, wherein the isosbestic light signal includes one of a near infrared light signal and a green light signal.
13. The system of claim 10 , wherein the first value is a maximum of the intensity of the red light signal, the second value is a maximum of the intensity of the infrared light signal, and the third value is a maximum of an intensity of the third light signal.
14. The system of claim 10 , wherein the first additive component and the second additive component are determined based on an empirically-derived lookup table.
15. The system of claim 10 , wherein the at least one processor is further operable to map physical conditions, the physical conditions including a location of the at least one optical sensor relative to the human tissue and a pressure of the at least one optical sensor on the human tissue, to values of the first function, values of the second function, and values of the third function by repeatedly performing the following operations:
receiving an indication that the physical conditions are changed due to displacing the at least one optical sensor relative to the human tissue;
receiving, via the at least one optical sensor, the red light signal, the infrared light signal, and the third light signal for a pre-determined period of time;
determining, based on the red light signal, a value of the first function;
determining, based on the third light signal, a value of the second function; and
determine, based on the infrared light signal, a value of the third function.
16. The system of claim 10 , wherein the at least one optical sensor is configured to be placed on a fingertip to measure a PPG, the reference PPG waveform being obtained based on the PPG.
17. The system of claim 10 , wherein at least one of the similarity measures is determined using
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wherein {right arrow over (w)} is data representing the waveform of the red light signal, and {right arrow over (ƒ)} is data representing the reference PPG waveform.
18. A non-transitory computer-readable storage medium having embodied thereon instructions, which when executed by a processor, perform steps of a method, the method comprising:
receiving:
a red light signal reflected from a human tissue of a patient, the human tissue including a pulsatile tissue and a non-pulsatile tissue, the red light signal being associated with a red wavelength;
an infrared light signal reflected from the human tissue, the infrared light signal being associated with an infrared wavelength; and
a third light signal reflected from the human tissue, the third light signal being associated with a third wavelength, the third wavelength being different form the red wavelength and the infrared wavelength;
determining, based on the red light signal, a first value of a first function-invariant to an oxygen saturation in the pulsatile tissue;
determining, based on the infrared light signal, a second value of a second function invariant to the oxygen saturation in the pulsatile tissue;
determining, based on the third light signal, a third value of a third function invariant to the oxygen saturation in the pulsatile tissue;
determining a first additive component in the red light signal and a second additive component in the infrared light signal, wherein the determination is based on the first value, the second value, and the third value, and wherein the first additive component and the second additive component are due to reflection from the non-pulsatile tissue;
removing a first non-pulsatile component from an intensity of the red light signal to estimate a first corrected intensity;
removing a second non-pulsatile component from an intensity of the infrared light signal to estimate a second corrected intensity;
calculating, based on the first corrected intensity and the second corrected intensity, a ratio of a red light absorption coefficient and an infrared light absorption coefficient;
determining, based partially on the ratio, at least the oxygen saturation in the pulsatile tissue;
acquiring a reference photoplethysmogram (PPG) waveform;
determining first similarity measures between a pre-determined number of waveforms of the red light signal and the reference PPG waveform;
determining second similarity measures between a pre-determined number of waveforms of the infrared light signal and the reference PPG waveform, the waveforms of the infrared light signal being detected concurrently with the waveforms of the red light signal;
calculating an average of products Ai×Bi to estimate an adequacy of the red light signal and the infrared light signal, wherein Ai are the first similarity measures, Bi are the second similarity measures, and i=1, . . . , N, wherein N is the pre-determined number of waveforms of the red light signal;
estimating, by the processor, an estimate of the adequacy of the red light signal and the infrared light signal, based on the average of products;
collecting, for a period of time, data concerning the red light signal, the infrared light signal, the third light signal, the adequacy, and the oxygen saturation;
analyzing the data to detect trends in the oxygen saturation; and
providing, based on the trends in the oxygen saturation, reports regarding a health status of the patient.Cited by (0)
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